The present invention pertains to a seal or shield to prevent transmission of electromagnetic radiation, particularly in the radio frequency range, along a shaft or outer tube of a coaxial cable penetrating a shielded enclosure.
Shielded enclosures or rooms are provided for shielding certain electrical equipment and communications devices from electromagnetic interference (EMI) and so called radio frequency interference (RFI). In many applications of shielded enclosures, it is necessary to penetrate the enclosure wall with a rotating or reciprocable shaft or a coaxial cable structure for various purposes. For example, in testing communications devices in a shielded enclosure, it is often necessary and desirable to be able to rotate o r reciprocate the device within the enclosure without placing actuators, such as electrical motors and controls therefor, within the enclosure itself. In this regard, drive mechanisms for rotating or reciprocating devices within a shielded enclosure have been mounted on the enclosure wall on the exterior thereof with a rotatable or reciprocable shaft penetrating the wall. Such penetration provides a path for transmission of EMI and RFI through the enclosure wall. Heretofore this type of transmission path has been isolated or shielded by so called labyrinth type shields. Labyrinth type shields or seals for EMI and RFI shielded enclosures are relatively complicated devices requiring close tolerance machining and assembly processes in order to ensure that an electromagnetic radiation signal on one side of the penetration is not detectable on the other side of the penetration of the enclosure wall. These precisely machined parts are subject to wear and the shielding performance of same tends to degrade over time.
Consequently, there has been a need and desire to provide improved means for shielding shafting and cable outer conductors or sleeves, for example, in applications where these devices must penetrate the wall of a shielded enclosure. Moreover, prior art devices and methods for shielding cylindrical shafts or cable outer sleeves do not suitably provide for a shaft or other structure which must be moved or reciprocated linearly along its longitudinal axis rather than rotated about such axis. It is to overcome the problems associated with prior art methods and structures for shielding or sealing the transmission of EMI and RFI that the present invention has been developed.
The present invention provides a shield or so-called seal mechanism to prevent the transmission of electromagnetic interference or radio frequency interference through a wall of a shielded enclosure which has been penetrated by a rotatable, or axially movable shaft, in particular.
In accordance with one aspect of the present invention, an electromagnetic radiation seal is provided for a rotatable or linearly movable, generally cylindrical shaft or tube penetrating a wall of a shielded enclosure to prevent transmission of electromagnetic interference or radio frequency interference through the wall by way of the shaft or tube.
In accordance with another aspect of the invention, an electromagnetic radiation seal is provided for a shaft or tube wherein an electrically conductive media is in intimate contact with the shaft or tube to redirect the radiation and prevent transmission of same into or out of the interior of a shielded enclosure penetrated by the shaft or tube. The seal also provides for supporting a rotatable or linearly movable shaft or tube on suitable spaced apart bearings. In one embodiment of the invention, the seal also includes axial shaft locating collars to prevent axial excursion of the shaft and to contain the conductive media. In another embodiment, rotation and/or linear reciprocation or oscillation of the shaft is permitted without loss of electromagnetic radiation sealing capability.
Those skilled in the art will further appreciate the above mentioned advantages and superior features of the invention together with other important aspects thereof upon reading the detailed description which follows in conjunction with the drawings.